Q: I have an 8GB iPhone. When I am on the phone for more than 30 seconds the screen goes black. I cannot hang up or do anything. I have to wait for the phone to figure out that I am off or the other person to hang up for the menu screen to return. The screen is completly black so you do not see the end call option. the home button at the center does not respond or work. This is also happening to my friend’s phone. Any suggestions?
A: The most likely cause of this problem is the iPhone’s proximity sensor that is used to turn off the screen when you hold the iPhone up to your ear during a phone call. This sensor is only active while you are on an actual phone call, and is triggered by the proximity of an external object to the earpiece (at the top of the iPhone). When this sensor is triggered, the iPhone screen goes blank the and is disabled to prevent accidental input from brushing up against your face.
Since the sensor is only active during an actual phone call, when the other party hangs up, the sensor is disabled, returning the iPhone to normal operation.
This sensor is located immediately above the actual iPhone earpiece, and is triggered by any object within about a one-inch proximity (you can find more information on Apple’s iPhone page at http://www.apple.com/iphone/features/index.html#sensor). iPhone cases that block this area could cause the sensor to trigger even when the phone is away from your face, as could significant dirt or smudging in this area. Normally a case should not be a problem as the sensor is not triggered if it’s already covered when you begin a phone call, but it’s possible for the top of the case to trigger the iPhone sensor if it moves even slightly. If you are using a case, try using the iPhone without the case and see if this behavior changes.
It should also be noted that this sensor is inactive when using speakerphone mode or wired or Bluetooth headsets, so this can be used to determine whether the proximity sensor is actually the problem.
If this is occurring without any obvious obstructions on the upper portion of the iPhone, then it is possible the proximity sensor itself is defective and you should look at getting the iPhone serviced.